The prior art of a padlock generally has a U-shaped lock and bolt 9 (shown as in FIG. 6) having unequal length legs. The longer of the two legs pierces through and protrudes the lock body 91 and the other leg of the U-shaped locking bolt 9 may be locked by protuberance 93 of a lock mechanism 92. Such a U-shaped locking bolt may be broken by force, and the lock is not easy to lock or unlock if the visibility is bad. Another kind of prior art has a rounded bow 8 (shown as in FIG. 7) which has two notches 81 at two ends. Both notches penetrate through and can be locked into two holes 82 of the lock body 89 which is a through bore and has an engaging member 84 and a lock mechanism 85 placed in the lock body 89. The lock body 89 has two openings 86 symmetrical with the two holes 82 of the lock body 89 and is controlled by a lock mechanism 85. However, if visibility is not good, the user may have difficulty placing the bow 8 into the two holes 82 of the lock body 89. In view of such shortcomings, therefore, the inventor has invented the present invention referred to as an improved padlock.